Polyurethane resin matrices are a type of highly crosslinked thermosetting high molecular materials which may be used for preparing polyurethane composite materials. Compared with traditional unsaturated resin and vinyl ester resin systems, polyurethane resins are characterized by excellent fatigue resistance and chemical corrosion resistance, superior impact toughness, low shrinkage and absence of styrene, etc. Hence, they are used in the composite material field more and more frequently.
The molding compound of unsaturated polyester resin or vinyl resin used in the prior art molding process may be stored for at least 3 months at 25° C. due to the addition of a polymerization inhibitor. In contrast, because of the extremely high activity of the isocyanate component, reaction will occur very quickly once polyurethane resin is mixed fully with a polyol component, leading to gelling and curing within several seconds to a couple of hours, such that the polyurethane molding compound loses mobility or becomes very stiff. As a result, the polyurethane molding compound is neither easy to be cut, nor can it be laid in a particularly shaped mold to be pressed into an article having a complex shape. Consequently, it can not be subject to molding. As such, the storage lifetime of a polyurethane molding compound prepared according the prior art process is generally no longer than 24 hours, which limits the use of a polyurethane composite material in a molding process badly.
On the other hand, a molding process in which unsaturated polyester resin or vinyl resin is used entails a large quantity of small molecular reactive monomers containing vinyl group, such as styrene, diphenylethylene and methyl methacrylate. When the molding process is completed, there are still a lot of residual small molecular monomers which become a source of VOC (volatile organic compounds), bringing about a high TVOC (Total Volatile Organic Compounds) value to these composite materials and producing pollution which is harmful to the health of the users.
CN1327456A discloses a polyurethane molding body and a process for preparing the same, wherein the polyurethane composition comprises: a component comprising an unsaturated bond and an active group which is reactive to isocyanate, and a component comprising isocyanate group; and discloses the use of the above components to prepare a free radical curable molding body.